1. Field of the Invention
The present invention relates to photoresist monomers, polymers derived from the same and photoresist compositions comprising the polymers. In particular, the present invention relates to norcamphor or camphor derivative photoresist monomers, polymers derived from the same, and photoresist compositions comprising the polymers that are suitable for photolithography processes employing KrF, ArF, EUV, VUV and similar light sources.
2. Description of the Background Art
Recently, chemical amplification-type DUV photoresists have been investigated to increase sensitivity in minute image formation processes for preparing semiconductor devices. Such photoresists are prepared by blending a photoacid generator and matrix resin polymer (i.e., photoresist polymer) comprising an acid labile group.
In a photolithography process, an exposure of photoresist to light of a particular wavelength generates an acid from the photoacid generator that is present in the photoresist. This acid causes the main chain or the branched chain of the resin to decompose or become cross-linked. In addition, the acid removes the acid labile group and changes the polarity of the photoresist in the exposed region. This polarity change creates a solubility difference between the exposed portion and the unexposed portion in a developing solution, thereby allowing a pattern formation. The resolution of the pattern that is formed depends on the wavelength of the light sourcexe2x80x94i.e., in general, a shorter wavelength allows formation of more minute patterns.
In general, a useful photoresist (hereinafter, abbreviated as xe2x80x9cPRxe2x80x9d) has a variety of desired characteristics, such as excellent etching resistance, heat resistance and adhesiveness. In addition, a photoresist should be easily developable in a commercially readily available developing solution, such as 2.38 wt % or 2.6 wt % aqueous tetramethylammonium hydroxide (TMAH) solution. However, it is very difficult to synthesize a photoresist polymer that satisfies all of these requisites.
A resin (i.e., photoresist polymer) like novolac resin having high transparency and high etching resistance at the wavelength of 193 nm has been investigated. In addition, researchers at the Bell Research Center have investigates improving the etching resistance by increasing the alicyclic units in the polymer backbone of the resin. Furthermore, Fujitsu and Sipri have studied the effect of adding methacrylate and/or acrylate monomers to improve the etching resistance. Unfortunately, the resulting polymers do not have satisfactory etching resistance. Moreover, the cost of producing polymers having increased alicyclic units in the polymer backbone is significantly higher. Furthermore, many photoresist polymers generally have low adhesiveness; therefore, the dense L/S pattern below 150 nm may collapse.
Recently, in an attempt to overcome some of the above-described disadvantages, Frechet et al. have prepared poly(spiro norbornane) having the following structure: 
Frechet et al., SPIE, Vol. 3333, 83, 1998. However, the poly(spiro norbornane) provides a resolution of only about 180 nm, and thus is not suitable for forming a minute pattern of high density.
The present inventors have found that adhesiveness of the resist (i.e., photoresist polymer) to a silicon wafer can be enhanced by introducing hydroxyl groups to the photoresist polymer. Furthermore, the present inventors have found that the solubility of such photoresist polymer in a developing solution can be easily adjusted by changing the amount of acid labile protecting groups in the photoresist polymer.
Accordingly, it is an object of the present invention to provide novel photoresist monomers having the excellent etching resistance, reproducibility, durability, adhesiveness and resolution.
Another objective of the present invention is to provide photoresist polymers derived from such photoresist monomers.
Yet another objective of the present is to provide photoresist compositions comprising such photoresist polymers.